Can you have a mix of 32 and 64 bit domain controllers?

I see this questions come up quite a bit about the interoperability of x86 and x64 domain controllers. Does replication work? Do the tools cross over well? Any gotchas that we should know about? Etc. Well I'm here to tell you that here at Microsoft we've been running a mix of 32 and 64 bit domain controllers since beta Wk23 SP1, and I can report back to you "Don't worry about interoperability of the domain controllers".

Replication works as expected.

Remote management tools connect the same.

When you TS everything feels the exact same.

You wont even know if its x64 or x86 unless you open up task manager and check out how much memory LSASS is using...

When I have engagements with customers, they ask if they should upgrade to x64 in their environment. My response is: that depends. Should you buy x64 compatible hardware? Yes, the cost difference is not that drastically different and this prepares you to install an x64 OS in the future. At the same time, an x86 OS installs and works as expected on the hardware, although you don't get all the nice benefits of running in true x64.

Do you need to spend tons of extra memory so that the DIT can be cached? That depends, and you can read this article for an explanation.

What if it’s not an application facing GC? As in a GC that is in a tail site that’s there for authentication requests? I don’t know if spending the extra money on RAM in that instance is really worth it.

If we’re talking about Exchange facing, then yes, the more you put in cache the better the perf for the queries coming in. No doubt.

Service Pack 2 is the first Service Pack that patches Windows Server 2003 and Windows XP Professional x64 RTM SKUs via a single update. In addition, Service Pack 2 also updates Windows Server 2003 R2 RTM release with a single install experience.

We (MSIT) never ran R2 on our domain controllers as there was no benefit. If you want to use ADFS and some of the other features on servers in your domain you’ll need to upgrade the schema for R2 so that the domain can support those new features.

R2 was a feautre pack, SP2 is an OS update with tons of hotfixes for many issues we’ve resolved with customers and internally.

Just to be clear: Windows 2003 R2 came out well over a year ago. Windows 2003 SP2 just got released a couple of months ago.

You must run the version of Adprep that is compatible with the version of the Windows server operating system that is running on the schema operations master—either the x86-based version or the x64-based version.

With a 4GB DC spec, the x64 OS can make the difference in terms of getting an extra gig of a DIT in memory – that’s a big performance gain. On a busy GC that’s a very worthwhile upgrade with no outlay (labor aside) involved…

Does the mix of 64 bit and 32-bit D.C.s affect R@ rollout and the extension of the AD schema. I noticed that there are two versions of the file to extend the AD schema depending on which you use for AD (32- or 64-bit). If you have both, how would you choose?

I have since read the differences about SP2 and R2 and I’m not sure we would use everything that is included in R2 anyway. Plus, I’m a little nervous about extending the AD schema. I know we’ll have to do that for Exchange soon, too.